A sensing head or feeler has been utilized in conventional measuring systems in which the sensing head or feeler is continuously displaced over a surface to be measured and its predetermined proximity to the surface is ascertained by sensing a physical contact or contact pressure between the relatively moving members. Difficulties have been encountered in sensing systems of this class in precisely determining establishment a given contact or proximity relationship especially where the members become sufficiently close that the rate of change in distance or contact pressure is minute and where the contact pressure cannot be precisely reliable.